This invention relates to a calibration device, a calibration method and a dry calibrator.
Profiles of thermoplastic materials (e.g. PVC) generally are manufactured by means of extrusion. Shaping of a profile requires a nozzle and a calibration device.
Calibration devices for manufacturing plastic profiles, e.g. window profiles, usually include a dry and a wet calibration device, wherein after exit from the nozzle the hot extrudate first passes through the dry calibration device and subsequently through the wet calibration device. At the end of calibration and after complete cooling of the profile to room temperature, the profile must have the desired contour, i.e. the profile must have the nominal dimensions.
The wet calibration device includes a plurality of vacuum tanks arranged in series, in which extensive cooling of the profile is effected by direct contact with the cooling water, after the same has partly been cooled already in the dry calibration. Usually, so-called short calibrators or covers are arranged in a vacuum tank of the wet calibration device at intervals of about 100 mm on the inlet side and about 500 mm on the outlet side, which each have a through opening which largely corresponds to the geometry of the profile.
The vacuum tanks as such are closed on all sides. Covers with openings for the entry and exit of the profile only are arranged at the end faces. The vacuum tanks are charged with negative pressure (order of magnitude about 30 to 100 mbar), whereby the profile is slightly “bloated” and rests against the through openings of the covers. The profile thus cools down in a defined shape, which ensures dimensional stability.
The cooling water flows through the vacuum tanks proceeding from few supply lines down to few discharge lines.
The negative pressure only must be applied via a negative pressure port and then each acts in the entire interior space of a vacuum tank. The manufacturing effort for the short calibrators (covers) is comparatively low, because the same do not require any supply and distribution bores for negative pressure and cooling water.
The dry calibration upstream of the wet calibration includes at least one dry calibration device, wherein e.g. up to eight dry calibration devices can be arranged in series.
The dry calibration devices include through openings with running surfaces for a contact with the extrudate, which approximately corresponds to the contour of the profile. In detail, however, dimensional or geometrical differences do exist, in order to follow the reduction in length with decreasing temperature of the plastic and in order to compensate the distortion as a result of different cooling rates.
The dry calibration devices are supplied with negative pressure and with cooling water. The negative pressure applied at the running surfaces effects that the profile is sucked against the same. The negative pressure acts via so-called vacuum slots between profile and dry calibration device and ensures that the profile rests against the running surface without clearance, so that said profile assumes a defined outer contour. Within the calibration, a flow connection to the vacuum pumps is created via connection and distribution bores. Outside the dry calibration devices, the transmission of the negative pressure is effected by means of hoses and connecting points.
As a result of the close contact of the profile on the running surface to the dry calibration device, a heat transfer from the hot profile to the cold dry calibration device is effected.
To prevent or minimize a rise in temperature of the dry calibration devices, the same are cooled, mostly continuously. This is effected by passing cooling water through cooling channels located close to the running surface. Each of these cooling channels requires a supply line and a discharge line for the cooling water, wherein it is possible however to combine several cooling channels. Thus, for each cooling circuit two water ports are required, each for the supply line and for the discharge line.
The maintenance of the desired operating state of the dry calibration devices requires a considerable additional effort during manufacture in addition to the required minimum requirement with regard to the geometry of the running surface, in order to be able to ensure and reproduce the required negative pressure and cooling, which in particular concerns the manufacture of distribution bores for the negative pressure and for the cooling water supply and discharge lines. Each port requires corresponding coupling points (couplings) and connecting hoses, which during a change of the calibration must be disconnected and connected with regard to a different profile geometry. In addition, certain settings with regard to the flow rate or height of the negative pressure must be maintained, whereby corresponding cocks also must be provided for each port. In general, the expenditure during manufacture and operation of the conventional dry calibrations is high.
It therefore is the object to create a calibration device which has a simple design and to create a calibration method which is easy to carry out.